The present invention relates to a fiberscope. More particularly, the invention relates to a fiberscope which is adapted to be inserted into a bodily passage, such as a blood vessel or the like, through which an opaque fluid, such as blood, passes to observe the interior of the passage.
A conventional fiberscope of the same general type to which the invention pertains, as shown in FIGS. 1 and 2, includes an illuminating light carrying optical fiber 7 passing through a flexible tube 1 to direct light from a light source 3 to a blood vessel wall 5, an image light receiving optical fiber 11 for directing light reflected from an image of the blood vessel wall and received through an optical system at the end thereof to an eyepiece assembly 9, and a liquid guiding passage 17 for guiding a transparent flushing liquid such as a normal saline solution from a syringe 15 to the tip of the fiberscope to form a transparent region between the blood vessel wall 5 and the tip of the fiberscope. Reference numeral 19 designates a branching mount.
The flushing liquid which forms the transparent region should be supplied at a flow rate Q.sub.F at least equal to the flow rate Q.sub.B of blood, that is, about 50 cm.sup.3 /sec. For example, where a blood vessel has an inner diameter of 10 mm, the blood flows at a speed of 64 cm/sec. In this instance, if it is desired to obtain a clear visual field for 0.5 sec., the required volume of the flushing liquid is 25 cm.sup.3. However, injection of such a large quantity of normal saline solution into the blood vessel in such a period of time may create a shock force which damages the vessel, while further the high pressure required to inject the solution might possibly force dissolved gas out of the solution, which is of course dangerous. For example, the initial velocity of the saline solution jetted from a flushing tube of an inner diameter of 3 mm is about 7 m/sec. This causes a strong shock to the blood vessel. Moreover, if a large quantity of normal saline solution is to be injected, the liquid guide passage must have a large cross section. This causes the overall diameter of the fiberscope tube to be large, resulting in disadvantages in that difficulties are then encountered in inserting the tube into the blood vessel to be examined.